The federal government paid $12 million for 1,718 District students to attend private schools as part of the city's voucher program last year, but it doesn't know where more than a fifth of them went, a Senate leader said at a hearing Wednesday.

The accusation came from Majority Whip Richard J. Durbin (D-Ill.) during a Senate Appropriations subcommittee hearing on the use of federal money in D.C. education. After being denied enrollment data from the group that oversees the D.C. voucher program, Durbin asked the 49 participating private schools how many voucher students each had educated last year. All but five schools responded -- but the numbers added up to only 1,334 students.

Durbin, who opposes the District's voucher program, also said he was concerned about oversight of the safety and academic records of some of the schools receiving federal money.

The vouchers cover up to $7,500 a year toward the cost of private schools for eligible D.C. students. Congress will decide this fall whether to extend the program. President Obama and Education Secretary Arne Duncan have said they support keeping vouchers available for students now receiving them but closing the program to new entrants.

Gregory M. Cork, president and chief executive of the Washington Scholarship Fund, the group that oversees the voucher program, said at the hearing that he had referred Durbin to the schools to get the enrollment information because of privacy issues.

"The only concern we have is about the confidentiality and the privacy of our students," he said.

But in an interview after the hearing, Cork said that he would provide Durbin with the enrollment data and that he would work to resolve the discrepancies between his and Durbin's numbers. He said that he hadn't seen Durbin's information but that it was possible that students had left the program partway through the school year, which might lead principals to report lower numbers than their initial enrollment.

At the hearing, Cork said that although he agreed that "the academic progress of the students is critical," his organization wasn't in a position to evaluate the schools' academics. He said he relied on the city to do building inspections and to make sure schools were physically safe.

D.C. Schools Chancellor Michelle A. Rhee, who testified at the hearing, said she supports funding charter schools and the voucher program. But she said she wants students receiving vouchers to take the same standardized tests as public school students to assess their academic progress, which isn't the case now.